Certain races, have the Scissors to my Rock. Certain races are the Paper to my Rock. I will always trump the Scissors, but I can't survive a run in with Paper. That is just how this game was developed. There are races that can get around Dodge, there are races that can plink plink plink a White Star to death with fighters.
Nerf the White Star, and you're helping Paper even more, and giving Scissors an advantage it didn't need.
The proposed change takes away one of my beam dice, if I do anything else. If I close blast doors, if I fire a second weapon, what have you. Well, unfortunatly the dice gods hate me, and if I only had one dice to roll, the odds of me rolling 4+ is just that much less likely. Holy Crap the White Star can get great numbers, well, that turn I fail to roll higher than a four... I did what... nothing?
There are statistics, and there is what makes the game fun. The White Star is toast if it loses its one arc, the white star dies horribly to fighters, and things that can ignore dodge. Yes, not everyone has those things, but if you nerf us, the things we already suck against, we're just going to suck more against, and I'll seriously retire my ships.
If I roll two dice, I might roll both, I might roll nothing. I tell you what though, when I do get that run away beam roll, it is something I think makes the game a lot of fun to play, and with just one dice to roll, I think the odds of having one of those fun explosive "holy crap!" moments becomes less and less likely.
Across the board the game is not balanced point for point. Certain things are just built to be better than others. You think ISA players think the Liati is fair? Why would a game of multiple armies, build a ship just to kill another ship? That isn't system wide balance, that is X vs Y balance, ignoring Z, W, and Q.
Everyone should have something to deal with everyone else, and until that is the case, this game will never truly come into balance, and remain a novelty for folks who got a kick out of the B5 series.